Many patients with private insurance who are taken to the hospital by ambulance also feel that they are being taken to the cleaners.

An investigation by Kaiser Health News (KHN) finds patients are stuck with exorbitant out-of-network bills because the ambulance companies and insurers had not hammered out a contract.

The ambulance companies say that they need to hike costs for rides because they keep crews on standby 24/7, and because Medicare and Medicaid do not pay enough. So they try to make up the lost revenue through billing private insurers.

KHN looked at 350 consumer complaints in 32 states after public outrage erupted over the unexpected bills. KHN found anecdotes that point to reasons for the outrage. For instance, in New Jersey, a man called 911 when he felt a burning sensation in his chest. He was treated at the scene by the ambulance crew and charged $2,100 for it.

“An older patient in California said debt collectors called incessantly, including on Sunday mornings and at night, demanding an extra $500 on top of the $1,000 that his insurer had paid for an ambulance trip,” KHN reported.

Even the fear of bad publicity does not seem to hold off the bill collectors. KHN looks at the case of Devin Hall, a 67-year-old retired postal worker. He is being charged an out-of-pocket fee of $7,109.70 by American Medical Response (AMR), the country’s largest ambulance provider.

His health plan, the Special Agents Mutual Benefit Association, said that he owes $727.08 for that ride, but in the meantime AMR sicced a debt collector on Hall, demanding the more than $7,000 fee. Hall has been trying to resolve the matter for months, and when KHN talked to AMR, AMR un-sicced the collection agency. But: “After further review, company spokesman Jason Sorrick said the charges were warranted because it was a ‘critical care transport, which requires a specialized nurse and equipment on board.’”

KHN’s story bolsters data collected by other venues. For instance, about a quarter of the 700 complaints about surprise medical bills submitted to the Consumers Union concern ambulance bills. About 1,200 complaints about ambulance service has been filed with the Better Business Bureau in the last three years, half of which were related to billing. Forty-six specifically mentioned out-of-network billing.

There are about 14,000 ambulance services in the United States. They are run by a variety of organizations, including government, hospitals, and private companies.